CCPR: Process quadratic flat edges without soft msaa

The artifacts previously thought to require msaa can be handled by
(1) converting near-linear quadratics into lines, and (2) ensuring all
quadratic segments are monotonic with respect to the vector of their
closing edge [P2 -> P0].

No. 1 was already in effect.

No. 2 is implemented by this change.

Now we only fall back on soft msaa for the two corner pixels.

This change also does some generic housekeeping in the quadratic
processor.

Bug: skia:
Change-Id: Ib3309c2ed86d3d8bec5f451125a69326e82eeb1c
Reviewed-on: https://skia-review.googlesource.com/29721
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
9 files changed